“Aquaponics is a method of combined fish and vegetable farming that requires no soil. The farmer cultivates freshwater fish (aquaculture) and plants (hydroponics) in a recirculating water system that exchanges nutrients between the two….The net result: a 90 percent reduction in freshwater use compared with conventional fish farming, and a significant reduction in added nutrients such as fossil fertilizers. The system can be run without pesticides and, because the fish environment is spacious and clean, without antibiotics.” (Roman Gaus)

“Aquaponics is the cultivation of fish and plants together in a constructed, re-circulating ecosystem utilizing natural bacterial cycles to convert fish wastes to plant nutrients. This is an environmentally-friendly, natural food growing method that harnesses the best attributes of aquaculture and hydroponics without the need to discard any water or add chemical fertilizers.” (The Aquaponic Gardening Community)

Aquaponics starts with fish food; fish are fed and produce waste. Bacteria convert the waste into nutrients that plants can absorb. Plants absorb the nutrients and filter the water for the fish. A water pump recirculates the system. An oxygen pump adds oxygen to the system. The only necessary nutritional inputs are the fish food and oxygen; the fish waste contains sufficient levels of macro- and micronutrients to produce hydroponic plants. Electricity is required to power the water pump, oxygen pump, and for environmental controls, such as greenhouse heating or cooling.

Plants
Leafy green herbs and vegetables do extremely well in aquaponics. Large fruiting vegetables are also applicable, including tomatoes, peppers, eggplant, and cucumbers, peas and beans. Root crops and tubers are less commonly grown and require special attention. (Somerville, et al, 2014)

Plants yielding fruit (tomatoes, bell peppers, and cucumbers) have a higher nutritional demand and perform better in a heavily stocked, well established aquaponic system. (Rinehart, 2010)

Three types of hydroponic beds are most commonly used to raise plants in an aquaponic system: 1) media-filled grow bed; 2) deep water culture (a.k.a. “raft” system); and 3) nutrient film technique. Each has its own advantages and disadvantages, and systems can be used interchangeably. Some aquaponic systems incorporate more than one of these hydroponic method for the plant side of the equation.

The media-based grow bed is a hydroponic trough filled with inert substrate like clay, perlite, pumice or gravel, serving as root support and microbial substrate.

The deep water culture (a.k.a. “raft” system) consists of large troughs of water with perforated floating rafts on top, in which net plant pots are inserted. In the this system, these plant pots are generally filled with media like coco, rockwool, or pumice that support the roots, which are then continually submerged in the water tank.

The nutrient film technique consists of narrow channels of perforated pipes where the roots are partially immersed in a thin layer of streaming water. Nutrient Film Technique can be used for vertical grow towers.

Fish
Several warm-water and coldwater fish species are adapted to recirculating aquaculture systems, including tilapia, trout, perch, arctic char, and bass. However, most commercial aquaponic systems in North America are based on tilapia. Tilapia is a warm-water species that grows well in a recirculating tank culture. Furthermore, tilapia is tolerant of fluctuating water conditions such as pH, temperature, oxygen, and dissolved solids. Tilapia produces a white- fleshed meat suitable to local and wholesale markets. (Rinehart, 2010)

Another benefit of tilapia is that it can subsist on a plant based diet, which saves on input cost and environmental strain. Advanced aquaponic operations may breed their own fish. However, most purchase baby fish fry from local suppliers. The maximum fish stocking density is around 1 lb per gallon, though it is not uncommon for large producers to exceed that number.

The amount of plants in your system dictates the minimum you need to feed your fish; the fish must produce enough waste for the plants (and there must be enough bacteria to convert the waste). The feed rate ratio for leafy vegetables is 20–50 grams of food per meter squared of grow space per day. The feed ratio required for fruiting vegetables 50–80 grams per meter squared per day. (Somerville, et al 2014)

Tilapia information: Tilapia is the world’s second most farmed fish (after carp)—and the fourth most consumed type of seafood in the U.S. (after shrimp, tuna, and salmon). (berkeleywellness.com)

Tilapia is a white-fleshed freshwater fish that’s mild in flavor, which makes it appealing to people who don’t like “fishy” fish. It’s relatively low in calories (130 per 3.5-ounce serving, cooked) and rich in protein (26 grams). But if you’re looking for a lot of heart-healthy omega-3 fats, tilapia is not a good choice. It has very little fat—2 to 3 grams per serving, of which less than 0.2 grams is omega-3s (in contrast, both wild and farmed salmon have more than 1.5 grams of omega-3s per serving). Farmed tilapia is particularly low in omega-3s because its diet is predominantly corn- and soymeal-based, in contrast to the omega-3-rich algae and other aquatic plants that wild tilapia feed on. (berkeleywellness.com)

Bacteria
In aquaponics, ammonia from fish waste must be oxidized into nitrate to prevent toxicity to fish. The nitrification process is a two-step bacterial process where ammonia-oxidizing bacteria convert ammonia into nitrite, and then nitrite-oxidizing bacteria convert nitrite into nitrate. The five most important factors for good nitrification are: high surface area media for bacteria to grow and colonize; pH (6–7); water temperature (17– 34°C); dissolved oxygen (4–8 mg/litre); cover from direct exposure to sunlight. (Somerville et al, 2014)

Neither fish nor plants can live in an aquaponic system without an adequate level of bacteria. The bacteria in an aquaponic system are housed on a biofilter, which is a fancy name for anything that has a large amount of surface area relative to volume for the bacteria to colonize. There are many materials that aquaponic growers use as biofilters, including volcanic gravel, expanded clay, commercial plastic biofilter balls, bottle caps, or mesh materials. Aquaponic systems using media-based grow beds do not require a separate biofilter apparatus because the media base has enough surface area. But in deep water culture systems, or nutrient film technique systems, the biofilter is a deliberately installed component to house the bacteria. A biofilter will often be housed in a separate tank, though there are systems in which the biofilter is in the tank with the fish.

Water
Water is the life-blood of an aquaponic system. It is the medium through which all essential macro- and micronutrients are transported to the plants, and the medium through which the fish receive oxygen. Thus, it is one of the most important topics to understand. Five key water quality parameters are: dissolved oxygen (DO), pH, temperature, total nitrogen, and water alkalinity. Each parameter has an impact on all three organisms in the unit (fish, plants and bacteria), and understanding the effects of each parameter is crucial. (Somerville et al, 2014)

System Construction
The vast majority of aquaponic systems are uniquely designed and constructed. Equipment can be purchased from hardware stores; boutique aquaculture or hydroponics supply stores; or recycled from industrial materials. Large aquaponic growing operations use wood or poured concrete to construct multi-thousand gallon water tanks. Aquaponic-specific supply and/or service businesses are becoming more common. A small number of these retailers sell pre-fabricated aquaponic systems, Nelson and Pade from Wisconsin being one of the largest and most visible.

Human ingenuity has provided countless variations on the basic theme of aquaponics. At its most basic sense, aquaponics is simply putting fish and vegetables in different containers with shared oxygenated water. Old water tanks, bathtubs, plastic barrels, wood and metal parts can all be used when building an aquaponic unit. Rafts and planting cups for [deep water culture] systems can be constructed from bamboo or recycled plastic; and media systems could be filled with locally available gravel. (Somerville et al of ’em, 2014)

Aquaponics includes a wide variety of systems, plants, and fish that are combined in a variety of ways. Each system has different types and levels of costs and returns. In spite of the variability, there are three general types of systems: raft or deep water culture systems, nutrient film systems, and systems based on media-filled beds. Raft culture typically is preferred for commercial operations, while the nutrient film technique (NFT) used for hydroponics is restricted to certain types of plants (like leafy green vegetables) that do not have large, heavy root systems. Both raft and NFT systems require that solids be removed. Media-filled beds are more commonly used for home-based aquaponics gardening and require lower stocking rates than those used in raft systems. (Engle, 2015)

System Startup
System cycling is the initial process of building a nitrifying bacteria colony in a new aquaponic unit. This 3–5 week process involves adding an ammonia source into the system (fish feed, ammonia-based fertilizer, up to a concentration in water of 1-2 mg/litre) in order to stimulate nitrifying bacteria growth. This should be done slowly and consistently. Ammonia, nitrite and nitrate are monitored to determine the status of the biofilter. (Somerville et al, 2014)

The ammonia naturally attracts the appropriate bacteria necessary for the biofilter; there is no need to add anything to the water to start the biofilter except for the tantalizing ammonia that hungry bacteria simply can’t resist. However, to skip this multi-week natural process, aquaculture retailers sell living nitrifying bacteria. Once added to the unit, they immediately colonize a system thus avoiding this cycling process. Or, if another aquaponic system is available, it is extremely helpful to share part of the biofilter as a seed of bacteria for the new System. (Somerville, et al 2014)

Greenhouse
Except for small hobby systems, most aquaponic systems are in a greenhouse. Two of the biggest reasons for the greenhouse are:

Aquaponic systems have high upfront capital costs, and are technically rigorous to design, construct, maintain, and operate. For most growers, this investment warrants yearlong food production. Yearlong food production requires a climate controlled greenhouse in most climate zones.

Leaves, bugs, sticks, extreme weather, outdoor effluvium, or other outdoor hazards can interfere with the water pumps, oxygen pumps, electricity, or system plumbing. A temporary power outage, clog, or leak that disrupts the system for even a short period of time can cause a grower to lose months of fish and crops. A greenhouse with a secure power source will greatly cut down on these risks.

Legal Issues
Zoning regulations and permits vary greatly from state to state, county to county, and city to city. Depending on your location and municipality, you may have to get and maintain certain licenses and/or permits….Also, be sure to check with your state department of agriculture or aquaculture to see what you may need to comply with for the fish element of your business. (Green Acre Aquaponics)

Aquaponic operations can also be GAP certified (good agricultureal practices), which means that the products are handled in the safest manner possible and have methods of traceability in place to insure food safety.

Researchers at Johns Hopkins University describe the legal considerations they undertook for their aquaponic system: “Consistent with state regulations for commercial finfish aquaculture operations, a permit was obtained from the Maryland Department of Natural Resources. The permit requirements included a site inspection, a map of the location, fish health certification and species origin documents, a plan for the treatment of non-native species to prevent introduction into the wild, a waste management plan, and annual reporting of activities under the permit. The DNR permit also allows for the commercial sale of live unprocessed fish.” (Love et al, 2015)

Is Aquaponics Organic?
There is some confusion in the aquaponic industry about whether aquaponics is applicable to be organic given the current legal paradigm.

Although the National Organic Standards Board developed a recommendation to prohibit organic hydroponics in 2010, the National Organic Program still has not adopted this formal recommendation. Because the National Organic Program has not issued guidance or regulations, some accredited certifying agents have augmented their revenue stream by going ahead and certifying hydroponic [and aquaponic] systems in the meantime. (www.truth-out.org)

“This process could not be more organic but getting a USDA organic certification for a culture system that does not use soil is tricky. A couple of commercial growers in the US have had their plants certified as organic. The USDA has not finalized organic certification standards for fish yet.” (Nelson & Pade)

“Aquaponics Gardening is necessarily organic. Natural fish waste provides all the food the plants need. Pesticides would be harmful to the fish. Hormones, antibiotics, and other fish additives would be harmful to the plants.” (Sylvia Bernstein)

In the absence of organic certainty, aquaponic growers recently gained an opportunity for another food certification. In February, 2016 Certified Naturally Grown (CNG), a non-profit organization offering peerreview certification to farmers, announced that they completed development of a new certification program for aquaponic producers and are now accepting applications. (cngfarming.org)